The past few years I've grown fond of Petunias in hanging baskets. In the Netherlands winters are relatively cold, so they will die outside. Beginning of October I took them inside with the plan to take cuttings and propagate them. I do this for the first time, and although I watched several Youtube videos and read stuff, I still have at least one important question.
This is the what I did until now. Took some baskets inside the house, and after a week of acclimatisation I took some cuttings, dipped them in rooting powder and put them in vermiculite that I kept most. The cups were placed inside a box with acrylic glass on top and a small heating mat underneath that I keep at 25°C (77°). Inside the box the temperature is a few degrees lower. I still keep the mother plants inside (under one or two household 17 W 2500 lumen LED lamps*) and they grow and flower like crazy. I cut out the flowers regularly to send more energy to branch and leaf formation (this is what I've read, don't know if it is correct to do so).
Some of the cuttings have done well so far and formed nice roots and look healthy. This one in the picture is now 38 days old, and today I transferred to a bigger pot with high quality potting soil…Now here comes my question:
When I look at the old mother plant, it is nicely branched very close to the surface (see photo 2). For me this looks like a desirable feature for a hanging basket, but I could be wrong…

Q: ---How did the grower of the plant get it to branch like this so near to the roots?--- (photo 2)
Thank you, and if you have any other tips, please let me know. This is new territory for me.
Greetings, Leo

* I have recently received a PAR meter, and the readings for the motherplants is 120-150 µmol/m2sec and 80 for the cuttings.

LeoLeo said:
When I look at the old mother plant, it is nicely branched very close to the surface (see photo 2). For me this looks like a desirable feature for a hanging basket, but I could be wrong…
Q: ---How did the grower of the plant get it to branch like this so near to the roots?--- (photo 2)

Welcome, LeoLeo!

I also often bring my petunias inside, where I let them grow, then I take cuttings for the next springs garden. I have a small hobby greenhouse I move them inside of in early spring to finish them off. It does look like you'll be successful as you are doing things how I would do them.

To answer your question, have a look at a "petunia culture" page where the seed/plug plant wholesalers are telling the professional growers EXACTLY how to make those baskets! (Link to that page in the quote boxes, below.) Think of this as the growers "recipe" to get their consistent crops. Much like a bread or soup recipe, if you follow it exactly, your petunia should branch exactly like the growers petunia.

The quotes I've shown is an example Petunia, so unless you've saved the tags and know EXACTLY the petunia you have, these instructions are only a broad example. If you do know the exact variety of petunia you have, you can look up the variety from the supplier and find that growers page for your variety.

Your answer: Pinching, lots of light (sunlight,) cool weather and Plant Growth Hormones (PGR's) as needed to reduce the "stretch" you are noticing- called 'internode length,' I believe. Look up those PGR's to find what they do...
Here it is for this variety I searched:

Ball FloraPlant said:
Propagation Guide:
Pinch: Recommended
Comments: Avoid stretch by moving crop to cooler air temperature in second and third weeks of propagation.
https://www.ballfloraplant.com...

Ball FloraPlant said:
Finishing:
Soil pH: 5.4-5.8
Light Levels (fc): 5,000-8,000
Temperature Day: 59-76°F (15-24°C)
Temperature Night: 53-61°F (12-16°C)
Fertilization (ppm N): 225-300
No. of Pinches: 0-1
Plant Growth Regulators (S=spray / (D=Drench: B-Nine(S) 1,500-2,500 ppm, applied 2-4 times, can be used to control habit early. Bonzi(D) 0.25-1.0 ppm applied as crop matures will control final height but not delay flowering or reduce flower size.
Comments: Cool temperatures and high light will reduce or eliminate any need for PGRs.
https://www.ballfloraplant.com...

Pretty specific, right? There's more on that page, like specific instructions for certain regions, like this:

Ball FloraPlant said:
BEST PRACTICES
West Region
Finish in an outdoor cold frame, where it can receive natural night temperatures as low as 32˚ F (0°C), but have some form of greenhouse roof protection to avoid frost exposure. PGRs in our trials were not needed when average daily temperature was below 54˚ F (12°C) in outdoor tunnels.
https://www.ballfloraplant.com...

Unless you have access to everything a professional grower has for the above instructions, you'll have to improvise. I doubt you'll be using the PGR's, so temperature control, pinching and lots of light (sunlight in a cold frame) might do the trick. Or don't bother with the stretching, and try to give them a shearing a few weeks before setting them out, which should force more branching, but perhaps delay flowering to much for your liking. Trial and error will be your guide.
Here's my early spring cuttings, still indoors under lights. This is after they've been transplanted from the covered flats I rooted them in, on a heat mat.

Here is the crazy mid-spring greenhouse. By this time the plants need the strong sunlight and cooler temperatures of my minimally heated greenhouse, while being protected from frost. You can see the flats of purple petunias mixed in with a bunch of fun things about mid-picture- I've sheared the top one-third of the plant by this point to increase the low branching, but I don't have a close-up picture. The stems I shear off, get re-stuck to make more!

Hope this shows it's possible, just keep trying to see what works.

Good luck. Share your results!

Hi Ken,

Thank you Ken for your detailed answer on your procedure! The example "petunia culture" page clearly shows how much effort is put into keeping the plant compact. This is very interesing. The info on PGRs is interesting as well. According to some of this info pinching should also work to stimulate branching.

My goal is to have baskets ready to hang outside 1-15 May, let's say week 19. According to some of these schedules, I would have to start with cuttings (URCs 'unrooted cuttings' as they call them in some guides 😊) 14 weeks earlier, so around 1st of February.

Can you tell me when you start cuttings and transplant?

I'm gonna keep experimenting: new cuttings, cuttings of my new little plants like you do, pinching, maybe some temperature control to finish off etcetera. Unfortunately I don't have such a nice greenhouse as you have, maybe I will make a cold frame out of one of my raised beds (mid March?).
It's clear that I still have enough time left before May! So far I have tried to document my steps as well as I can (with pictures and notes) and will keep doing this to learn.

I will also read some more on fertilisation. I started my cuttings in vermiculite, and once or twice I added very small amounts of fertiliser. I have now transferred my first rooted cutting to a fertilised potting soil that has nutrients for 6-9 weeks. Bought this from a local professional greenhouse where I bought some of the motherplants. His plants always grow well, and it's the same soil he uses to grow his plants. Do you use fertilised soil for your first transfer?

Thanks for putting me on track with this type of professional information. Together with stuff we can do as hobbyists I'm now more confident in a good outcome! Will update here or somewhere on this forum when I have interesting info.

Greetings and happy gardening!